Side fold sack with roll bottom

ABSTRACT

A side fold sack of polyolefin material that includes a tubular segment having side folds between front and rear walls of the tube. The bottom of the sack exhibits at least one fold of the tubular segment made at 180° about an axis which is generally transverse to the side folds. At least part of the folded area is covered with a label that provides support to the bottom of the sack.

The invention relates to sacks according to the preamble of claim 1.

Such type of sacks are known. For instance, DE 101 06 289 A1 shows such a sack. Among the disadvantages of the sacks fabricated with this type of simple fabrication procedure belongs that the bottom fold opens up particularly then, when the filled sack is stacked and the fold is exposed directly to mechanical load. Such mechanical load can include that another heavy, filled sack is dragged by this bottom fold, leading to breaking open of the fold. Therefore, the underlying problem of the invention was to propose a sack, in which the bottom area exhibits greater durability. This problem is solved by the characterizing features of claim 1.

Among the other advantages of such a sack belongs, that due to the presence of the bottom cover, the filled sack readily assumes a cuboid or a box-shaped form. Especially firm are sacks made from polyolefin material. For that purpose, the polyolefin fibers are in general textured and oriented mostly monoaxially, that is along their longitudinal axis. These fibers are often entwined into flat sheets, from which, tubes are later produced. However, the fibers can be processed directly to round tubes. This polyolefin material and its properties are well-known. It is explained, besides other publications, in WO 95/30598. Further processing of this material requires in-depth know-how.

Thus, for instance, it is necessary to follow certain processing steps during the welding of these sacks, in order to not lose the firmness of the oriented material again. The aforementioned publication also contains the details about that topic as well as about the used temperature ranges.

All the same, the heat induced seaming procedure in connection with the processing of the sack according to the invention is especially of advantage. Heat induced seaming means here a method of bonding, which requires supply of heat. That is, even a gluing method, which is carried out with temperature-dependent adhesives also belongs to a heat induced bonding method. The same applies to any other type of processing of the extrudates.

Especially advantageous are however the joint welding methods, in which the polyolefin fabric is bonded. Thereby, attention must be paid, as mentioned, that the firmness of the polyolefin fabric does not get impaired due to monoaxial orientation of the macromolecules in polyolefin bands.

A further advantageous possibility in the processing of this material lies in that, the coating, which is often made on polyolefin band tissues, is welded. The fabric is often coated in order, in particular, to the tissue more tight in the filling of pulverizable material.

The sack according to the invention exhibits a bottom fold, which is made about an axis, which is essentially transversal to the axis of the tubular segment or an area of tubular segment. Such a fold or a rolling is not easy to make. Even this fold or the rolling contributes to the subsequent box-like shape of the filled up sack and is therefore of special advantage. With a double fold, not only the stability, but also its tightness of the bottom area is increased considerably and to a surprisingly remarkable extent. The double fold leads to a still stronger bottom, which also supports the box-like shape of the sack especially in conjunction with the label. During the deposition of the label, care must be taken that at least parts of the bottom fold are covered with the label, so that the fold is supported by the label. Depending on the label, however, it can be adequate, if most of the areas remain unsupported and if the labels, for example, in the form of adhesive bands, cover only some parts of the areas of the fold.

For the fabrication of the sacks according to the invention, such tubular segments are suitable, which exhibit straight and/or staggered cuts. Sacks according to the invention with straight cuts are especially simple to fabricate. A preferred area of application of the sacks according to the invention lies in the storage and transport of bulk goods, especially of powder-like goods. In this area of its application, sacks, which also exhibit a box-like form, are common, but which are provided with a folded block bottom. Manufacture of such sacks is very elaborate. Common in this area of application are also cross bottom sacks.

In context of the present publication, bonding process is used to mean anything, in which materials are joined with each other. Explicitly mentioned already were the bonding and gluing processes, as well as joints of plastic parts with extrudates. Various materials can be used as labels, depending on the requirements in regard to the stability of the sack. These materials can be the same as or different from the material of the sack or the material of the tubular segment. In case of particularly high loads, olefin fabrics can be used. Again, here too, the modalities involved in making the joints, or the processing conditions recommendable in the processing of polyolefin fabrics, should be adhered to. In that context, reference is made again to the publication WO 95/30598. Especially advantageous thereby in the fabrication of the seams is, if the outer layer of the tube or the sack material is joined by melting. The heat necessary for that can thereby be supplied by means of heated air, which is blown on the seams to be jointed.

Further exemplary embodiments of the invention follow from the objective description and the claims.

The individual figures show:

FIG. 1 Perspective view of a tube or a segment of the tube in the fabrication of a sack according to the invention.

FIG. 2 Side view of a segment of the tube, in which an end is rolled inwards.

FIG. 3 Top view of an end of a sack according to the invention.

FIG. 4 Side view of an end of a sack according to the invention.

FIG. 1 shows a perspective view of a tube 1 or a tubular segment, which is suitable for the fabrication of a sack 2 according to the invention. In the exemplary embodiment, the tube 1 exhibits a longitudinal seam 3. As a rule, the tubes are in general fabricated with such a lengthwise seam from a flat sheet. Alternatively, the tube 1 can also be of a round shaped material, so that no lengthwise seams are there. The tube 1 shown in FIG. 1 exhibits side folds 4, made with depth A (see FIG. 3), between the front wall 5 and the rear wall 6 of the tube 1.

One step in the fabrication process of the sacks 2 according to the invention is illustrated in FIG. 2. About one axis, which runs transversally to the lengthwise seam 3 and lies in the plane parallel to the walls 5 and 6 of the tube, the lower end of the tube 8 is folded or rolled. Thereby, the folded end 8 of the tube comes to lie against the front wall 5 of the tube 1 or the sack 2 (as shown) or on the rear wall 6 (not shown). In each, two layers, which are laid one above the other by folding over or rolling, can be connected through an appropriate bonding process.

After the rolling up or folding of the end 8, a label 9 is connected with the folded end 8, and on the wall, on which the fold or the roll lies. In the example shown in FIGS. 3 and 4, the label 9 is connected with the lower end 8 and with the front wall 5. The label 9 extends over the entire length of the sack 2 or the tube 1. In the shown exemplary embodiment, the width B of the label 9 is somewhat smaller than the depth A of the side folds. If the width of the label 9 is smaller or equal to the depth A and the side edge of the label 9 is arranged near the fold—or the axis of the roll, then the label 9 lies exclusively at the bottom area of the sack, if it assumes, for example due to filling, a block-like shape. In that case, the bottom is also very resilient against mechanical loads, even when the sack is filled up. In order to improve the firmness further, it can be so provided, that the rolled up or the folded end 8 extends over half of the width B of the label 9. List of Reference Symbols  1 Tube  2 Sack  3 Longitudinal seam  4 Side fold  5 Front wall  6 Rear wall  7 Axis of the fold or the roll  8 Lower end of the tube  9 Label A Depth of the side folds B Width of the label 9 10 11 12 13 14 15 16 17 18 19 20 21 22 

1. Side fold sack from polyolefin material, which exhibits following features: an area of a tubular segment, with front walls and side walls of the sack, whereby the side walls exhibit side folds, a bottom area at an end of the area of the tube segment, which exhibits at least one fold of the tube piece material made at 180° about the axis, which runs essentially transversally to the side folds, characterized by a label, which covers at least parts of the folded area.
 2. Side fold sack according to the preceding claim, characterized in that the sack material includes fabrics of oriented polyolefin material.
 3. Side fold sack according to claim 1, characterized in that the joints of the label with the tube material, and/or of the flapped over tube material with at least one wall of the segment of the tube material, are heat induced.
 4. Side fold sack according to claim 1 one of the preceding claim, characterized in that at least one bottom area comprises two folds of the tubular segment material folded at 180° about an axis, which runs essentially transversally to the side folds.
 5. Method for fabrication of side fold sack, in which segments of a side fold tube are provided and in which in at least one end area of the segment, a fold of the tubular segment material is made at 180° about an axis, which is essentially transversal to the side folds, characterized in that at least parts of the folded regions are covered with a label.
 6. Method according to claim 5, characterized in that the bonding processes, which lead to the seaming of the folded tubular segment material with at least one wall of an area of the tubular segment and or the bonding processes which lead to the seaming of the flapped over tubular segment material with the label, are heat induced at least in part.
 7. Method according to the preceding claim, characterized in that the heat for the heat induced bonding process is supplied at least in part by means of air.
 8. Method according to claim 6, characterized in that at least a part of the coating made on the sack material is bonded by melting by means of heat.
 9. Method according to claim 5, characterized in that the sack is made from a tube segment.
 10. Method according to the preceding claim, characterized in that the tube segment is made from a tube with staggered cuts and/or straight cuts.
 11. Side fold sack according to claim 2, characterized in that the joints of the label with the tube material, and/or of the flapped over tube material with at least one wall of the segment of the tube material, are heat induced.
 12. Side fold sack according to claim 2, characterized in that at least one bottom area comprises two folds of the tubular segment material folded at 180° about an axis, which runs essentially transversally to the side folds.
 13. Side fold sack according to claim 3, characterized in that at least one bottom area comprises two folds of the tubular segment material folded at 180° about an axis, which runs essentially transversally to the side folds.
 14. Method according to claim 7, characterized in that at least a part of the coating made on the sack material is bonded by melting by means of heat.
 15. Method according to claim 6, characterized in that the sack is made from a tube segment.
 16. Method according to claim 7, characterized in that the sack is made from a tube segment.
 17. Method according to claim 8, characterized in that the sack is made from a tube segment. 